The present invention relates generally to gasoline service station equipment, and particularly to transitioning connections between an underground fuel storage tank and an above-ground fuel pumping apparatus.
Gasoline pumps are commonly located on raised concrete islands surrounded by pavement, and gasoline is delivered from an underground tank to the gasoline pumps through an underground pipe system extending to a point underneath the pumping island. This system includes a nominally horizontal main section and an upwardly curving end section for transition from an essentially horizontal attitude to a vertical attitude. A rectangular casing is embedded in a mass of concrete directly above the vertical portion of the upwardly curving pipe section, and the upper end of the pipe section extends to or through the bottom wall of the rectangular casing.
A vertically oriented safety valve is located within the casing in liquid connection to the vertical portion of the upwardly curving pipe section. The safety valve is designed to automatically close the pipeline in the event that an automotive vehicle should strike the above-ground pumping apparatus, which is located directly above the safety valve on the concrete island. The upper end of the safety valve housing has a narrowed annular neck section that will shear off in response to a horizontal striking force such as that generated when an automotive vehicle strikes the above-ground pumping apparatus. The safety valve includes an internal poppet valve element that is held open when the pumping apparatus is operating normally. When the upper end of the valve housing shears off, the poppet valve element is automatically biased to a closed position. This valve action prevents liquid fuel from flowing out of the pipe system onto the concrete where it could be ignited to possibly generate an explosive-type conflagration, or could seep into the ground.
During extended periods of service, leaks can sometimes develop in the underground piping system, particularly at certain pipe joints where the aforementioned upwardly curved piping section connects with the essentially horizontal underground pipe or the safety valve. The connection between the safety valve and the curved pipe section extends upwardly through the bottom wall of the aforementioned rectangular casing. If the leak occurs above the casing bottom wall, the casing will contain any liquid fuel that might tend to leak from the joint between the curved pipe section and the safety valve. The casing is equipped at its upper edge with an access plate that can be removed to permit a technician to inspect the joint between the curved pipe section and the safety valve. It thus becomes possible to repair a leaking joint within the casing.
However, pipe joints below the casing bottom walls and at the lower end of the curved pipe section are concealed or otherwise located underground a significant distance--e.g., approximately fifteen inches below the bottom wall of the rectangular casing. It thus becomes difficult to detect a leaking joint below the casing or at the lower end of the curved pipe section. Small quantities of gasoline leaking out of the earth-covered joint can, over time, cause significant ecological pollution damage. The gasoline can migrate through the earth to areas remote from the service station. Gasoline-contaminated earth is required by law to be dug up and hauled by truck to disposal sites in order to alleviate the effects of the underground leakage.
The upwardly curved transition pipe section is usually constructed of elastomeric or plastic materials reinforced with woven steel strands, such that the pipe section has limited flexibility. In order for the curved pipe section to make a ninety degree bend, the semi-flexible pipe section is required to be relatively long, such as twenty-four inches to thirty inches. The relatively long curved pipe section length results in the lower end of the curved pipe section being a substantial distance below ground level.
The underground gasoline storage tank is usually some distance away from the pumping station island, and often there is a distance of one hundred feet or more between the underground storage tank and the pumping station island. The nominally horizontal pipe between the underground tank and the upwardly curved pipe section is required to have an upward slope of at least one-eighth inch per foot of pipe so that liquid fuel will automatically drain back toward the tank, rather than from the tank toward the pumping apparatus. The required slope of the nominally horizontal pipe section causes the tank to be buried a considerable distance below the ground surface. Extensive excavation expense is therefore sometimes involved to repair leaks associated with the underground tank. The situation is aggravated by the fact that the upwardly curved pipe end section is required to be relatively long in the vertical direction.
The present invention provides a redesigned upwardly curved transition pipe section into an S-shaped transition pipe system having a relatively small vertical dimension. By reducing the vertical dimension of the transition piping, the depth of the underground fuel storage tank is reduced and the associated expenses of installation and removal are substantially reduced. This becomes especially important when it is necessary to excavate the area in an effort to locate and repair an underground leak.
The invention contemplates an underground transition conduit piping system wherein a liquid-tight casing is located in a concrete base and has a side connection with a generally S-shaped transition pipe, the transition piping being located within a hollow shroud attached to the casing side wall. The transition piping extends laterally and then downwardly from the casing in order to connect with the nominally horizontal main section of the underground piping system.
The "side-mount" character of the transition piping enables the associated pipe joints to be accessible from above ground, thereby enabling the detection and repair of leaking joints to be more easily accomplished without excavation or removal of the liquid-tight casing. Additionally, the vertical dimension of the transition piping is somewhat reduced, thereby reducing the required depth of the underground fuel tank.